When a wellbore is no longer producing, the wellbore may be prepared for abandonment. A segment of the casing is removed to form an openhole section of the wellbore. The openhole section is then plugged, and the wellbore is abandoned. To remove the segment of the casing, a tool string having a section mill coupled thereto is run into the wellbore. Once the section mill reaches the desired depth in the wellbore, fluid pressure is applied to the section mill via the through-bore of the tool string. The fluid pressure causes one or more blades to extend radially outward from the section mill and into contact with the casing. The section mill is rotated about its longitudinal axis (by rotating the tool string) causing the blades to cut through the casing. Once the section mill has cut through the casing, the tool string gradually lowers the section mill, and the blades mill the casing to remove the axial segment thereof.
As the blades mill the axial segment of the casing, the blades become worn down. Accordingly, oftentimes the blades of the section mill are only capable of milling relatively short segments of the casing, e.g., less than about 30 m, before they become worn down and ultimately ineffective. When longer segments of the casing need to be milled, the tool string and section mill are pulled out of the wellbore, a new section mill replaces the worn down section mill, the tool string and the new section mill are run back into the wellbore, and the above process is repeated to continue milling the casing. Replacing the worn down section mill during the milling process is time consuming, which leads to lost profits in the field.
Accordingly, what is needed is an apparatus and method for removing an extended (or longer) axial segment of a casing in a single trip downhole.